Hepatitis C virus (HCV) infection can result in varied clinical outcomes including acute hepatitis, chronic hepatitis, cirrhosis, and hepatocellular carcinoma. Chromic infections are common (>80% of these infected) and an estimated 170 million people are infected worldwide. Despite a great deal of progress, a vast number of unanswered questions remain concerning HCV replication, pathogenesis and immunity. One advance has been the construction of full-length HCV cDNA clones capable of producing infectious RNA transcripts, a technology which is essential not only for future studies on the molecular details of HCV replication but also for defining virus-host interactions that influence clinical outcome. Such RNAs are infectious after direct intrahepatic inoculation of chimpanzees, but attempts to demonstrate their replication in cell culture have met with limited success. In this proposal, microarray analysis will be used to define gene expression patterns in cells that are permissive for HCV replication. Liver resident human hepatocytes capable of supporting HCV replication in vivo will be compared to primary hepatocyte cultures, hepatoma lines, and hepatoma sublines that have been selected for their ability to support persistent replication of engineered HCV replicons. In a related study, the effect of HCV infection and/or protein expression on cellular gene expression will be assessed. Model systems will include cell lines and transgenic mice allowing tightly regulated expression of the entire HCV polyprotein or individual proteins, hepatoma sublines before and after transfection with functional HCV replicon, and infected versus uninfected hepatocytes from a SCID-Hu mouse mode, from chimpanzees, and form clinical material. This information will be used as a starting point for studying the impact of HCV on cellular responses to cytokines and other signals and regulating cell growth, apoptosis and host immune responses.